Gardeners have long been challenged to find an effective covering for the drain holes in planting containers. The drain hole must remain open to allow for the free passage of water out of the container. At the same time, the hole must also be covered in some way to prevent the egress of soil or planting medium.
The longstanding traditional answer to this problem has been to cover the drain hole with bits of gravel or broken pieces of old clay pots. However, these broken clay shards are becoming less available with increased use of planting containers made of plastic and synthetic materials. In addition, many urban and small-scale hobby gardeners in particular now find that they have neither the space nor lifestyle to maintain a stockpile of old broken pots or gravel solely for this limited purpose. Despite the shortcomings and decreasing availability of these materials, they are still the drain hole coverings widely recommended by expert gardeners, and virtually every book, magazine, and Internet website addressing the subject to date.
Such popular recommendations also often include the addition of a layer of gravel to the bottom of the pot, assuming that the unobstructed pathways of larger pore spaces will speed evacuation of water from the pot. However, observable soil mechanics and fluid dynamics argue against this practice. Modern agricultural and horticultural science has proven and teaches that water will not pass gravitationally from a finely textured soil mass into a markedly coarser underlying layer until the interface portion of the upper finer layer is fully saturated. The coarser the underlying material, the more difficult it is for water to move across the upper interface. Therefore, contrary to conventional wisdom, the addition of a coarse bottom layer actually impedes planting container drainage rather than promoting drainage.
The growing trend from clay pots to plastic and synthetic ones creates other challenges to gardeners. This change in materials technology greatly expands the possible profiles of planting containers, and the placement and number of their drain holes. Especially problematic are drain holes placed at the angle formed by a container's bottom and its vertical side wall.
Watering plants normally from the top erodes soil through the drain hole, but bottom watering and drenching do so even more. These two common horticultural practices involve placing filled planting containers directly in larger containers of water, for purposes of insect control or remoistening of overdried soil, and can erode the planting medium considerably over the life of the planting.
Bonsai gardeners have dealt with the problem of drain hole coverage by using small pieces of metal window screen, or similar material made of plastic. However, this improvisation is only effective with the very coarse soils used in this specialized field of horticulture.
The patent record describes a number of planting containers with a variety of configurations and compositions with no provision for the covering of their drain holes or channels. The following are offered as examples:                U.S. Pat. No. 4,329,814 issued to Blicha on 18 May 1982;        U.S. Pat. No. 4,356,665 issued to de Oliviera on 2 Nov. 1982;        U.S. Pat. No. 4,593,490 issued to Bodine on 10 Jun. 1986;        U.S. Pat. No. 4,644,686 issued to Whitman on 24 Feb. 1987;        U.S. Pat. No. 4,991,345 issued to Bloch on 12 Feb. 1991;        U.S. Pat. No. 5,446,995 issued to Huber on 5 Sep. 1995;        U.S. Pat. No. 6,138,411 issued to Lin on 31 Oct. 2000; and        U.S. Pat. No. 6,289,632 issued to Boling on 18 Sep. 2001.        
Bodine does consider the issue of soil loss through the drainage openings of his patented container. However, instead of a drain hole cover, Bodine specifies erosion baffles to impede the flow of water along the container's bottom and thereby control fine soil erosion to a limited extent.
Before beginning the planting process and enjoying any advantages offered by even the most improved containers, the individual gardener is thus required to solve the drain hole cover problem on his or her own. The following patents have attempted to address that problem.
An early invention, U.S. Pat. No. 611,523 issued to Springer on 27 Sep. 1898, teaches an imperforate disk or plate with a convex upper side and a series of radial grooves on its lower side, which converge into a depending stud which is to be inserted into the drain hole. Its rigid construction and direct fluid communication would not completely retain soil, and would not be effective for a drain hole located in an angular or concave area of a container.
Weidig's U.S. Pat. No. 1,453,216 issued on 24 Apr. 1923 calls for the insertion of a wire mesh baffle into the drain hole of a concrete planting container during the molding process. This device is clearly of limited use, being incorporated into the particular container under patent.
Wittbold includes a fragile paper drain hole cover in his U.S. Pat. No. 1,789,994 issued on 17 Jun. 1929 for a commercial plant transport container which can be later adapted as a permanent planting container by the customer upon purchase. At such time, the paper is intended to be manually ruptured, or degenerated by means of water contact. Once the paper seal is broken, no other means is provided for securing the soil within the drain hole.
The device of U.S. Pat. No. 1,869,606 issued to Mennell on 2 Aug. 1932 is a cap or disk molded integrally with a pot and centered over its drain hole. Water exits the pot through slots occurring at its angle of attachment. Its use is clearly limited to the specified container of the patent.
U.S. Pat. No. 1,884,204 issued to Pilkington on 25 Oct. 1932 teaches a drain hole cover of any number of intersecting and integrally formed curved resilient arms attached to one flat end of a small cylindrical member, the opposing flat end of which fits into the pot's drain hole. Its stated objective is to retard flow of water before allowing it to exit the container. This device is only useful in non-angular applications.
U.S. Pat. No. 2,026,679 issued to Higgins on 7 Jan. 1936 is for a drain hole cover of a vertical truncated cone shape with an open bottom end, and with a plurality of notches radially formed in its lower edge. Its open bottom and notched bottom edge rest on the container's interior bottom and fully cover its drain hole. This device is limited to use in flat-bottomed containers, and allows direct fluid communication.
U.S. Pat. No. 2,120,599 issued to Brown on 14 Jun. 1938 sets forth a vertical finned spindle joined to the center of a shallow receptacle by means of a threaded shaft. The spindle stabilizes the filled planting container in an upright position, while the vertical fins direct the outflow of water. This assembly is useful only with containers having a centered drain hole, and its complexity increases its cost.
U.S. Pat. No. 3,935,672 issued to Chatelain on 3 Feb. 1976 describes an upright, generally cylindrical structure which is placed over a planting container's drain hole, allowing drainage to occur only when the water level reaches the upper, open end of the cylinder. Consequently, there would remain in the bottom of the pot a stagnating, perpetually undrained volume of water equal in depth to the height of the cylinder. This invention encourages incomplete drainage and an overly wet environment, widely known to be detrimental to plants in containers.
U.S. Pat. No. 4,138,803 issued to Sherlock on 13 Feb. 1979 describes a container employing a completely obstructive drain plug. A perforated plate rests horizontally inside the container and somewhat above the obstructed drain hole. This allows a small volume of water to collect beneath the plate, providing beneficial moisture to plants during the brief period of commercial transport. For long term health, however, plants would need to be freed quickly from such a water-retentive environment.
U.S. Pat. No. 4,571,883 issued to Shaw on 25 Feb. 1986 describes a perforated cylindrical structure with a hemispherical top, which is limited to use with a corresponding dedicated planting container. Therefore this drain hole cover is not universally useful.
U.S. Pat. No. 4,860,491 issued to Panuski on 29 Aug. 1989 relates to a molded plastic disc with a plurality of arcuate openings and graduated standoffs. Its channels and openings are in direct fluid communication and therefore minimize erosion but do not prevent it. This drain hole cover is limited to use in planting containers with flat bottoms.
U.S. Pat. No. 5,448,854 issued to Hirsch, et al on 12 Sep. 1995 seeks to improve upon and simplify Shaw's complex device, but is still a somewhat complex molded plastic or ceramic configuration. Direct fluid communication between its passageways allows free drainage but does not protect completely against soil erosion.
The drain hole cover of U.S. Pat. No. 6,125,579 issued to Pavelka on 3 Oct. 2000 is limited to use in planting containers with elevated drain holes, and its inflexible molded plastic composition precludes its conformation to a variety of contours.
The planar device of U.S. Pat. No. 7,743,554 B2 issued 29 Jun. 2010 to Morris is elevated on three legs, and can only address drain holes located entirely on a container's lower horizontal surface. Its rigidity likewise renders it non-universal, since it may only be used in containers of a greater diameter than itself.
The above methods and devices offer no fully satisfactory answer to the need for an inexpensive, convenient, and universally useful drain hole cover for planting containers. The direct fluid communication common to the above methods and devices permit soil erosion to some extent during normal top watering and to a greater extent during bottom watering and soil drenching. Rigidity of material and particulars of configuration are limiting factors, and suggest looking to other more flexible materials to solve this problem. The following patents suggest such materials.
Brandell's U.S. Pat. No. 1,996,898 issued 9 Apr. 1935 presents a departure from rigid and solid materials. He specifies flexible, interstitial knitted metal mesh formed into a sleeve and folded in on itself to form a spongiform metal ball, which is placed over the drain hole in the base of the planting container. This allows water to drain freely and prevents the roots of the plant from clogging the drain hole, but is not stated to retain soil in the container. Furthermore, Brandell teaches no mechanism to keep the metal ball centered while the soil medium is being placed in the container. Most notably, depending on choice of metal, this device would possibly degrade in the constantly moist environment presented by a filled and watered planting container, either rusting or forming corrosive metal salts.
U.S. Pat. No. 3,675,368 issued to Nustad on 11 Jul. 1972 for a large rooftop planter box has a glass wool mat used primarily as insulation. This mat secondarily provides a drainage layer, presumably into which water can collect away from the planting medium, as no drain holes appear in the patent drawings. When handled, glass wool, often referred to as fiber glass, sheds tiny glass particles which are irritating to the skin. Therefore this would not be a material favored by consumers for drain hole cover application.
As a wire hanging planter basket may be considered a planting container with the spaces between the crossed wires constituting enlarged drainage voids, the following two patents are also considered prior art drain hole covers.
U.S. Pat. No. 3,958,365 issued to Proctor on 25 May 1976 specifies a loosely felted fibrous material consisting principally of coconut fiber to which a waterproof adhesive bonding substance has been applied, to be used primarily as a ground cover mat or soil cover. The biodegradability of the coconut fiber would eliminate this as an effective permanent drain hole cover solution.
The invention of U.S. Pat. No. 6,318,022 issued 20 Nov. 2001 to Just is a compressed sheet form of sphagnum moss which can be precut to fit planting containers in a variety of shapes. When moistened, the moss expands to its original natural thickness, and well retains soil within a basket's metal frame. While attractive in this application, sphagnum moss is well-known for its ongoing tendency to drop loose filaments. Also, such a biodegradable liner requires periodic replacement, a messy and inconvenient task.
Henson has submitted a patent application for a container lining, published as U.S. Patent Application Publication 2005/0060933 on 24 Mar. 2005. His invention is made from the fibers of the kenaf plant mixed with a binding agent. This liner could be used in either hanging baskets or pots, but like Proctor's, the base fiber would eventually biodegrade.
Materials described above will rust, irritate the skin or biodegrade, and still leave gardeners looking for a better alternative to cover their planting container drain holes. Man-made fibers present no such objections, however, and their compatibility with plant materials has been well established.
U.S. Pat. No. 3,866,352 issued to Herveling, et al on 18 Feb. 1975 is a pot liner made of a random nonwoven fiber mat of looped, intersecting and amorphous filaments of melt-spun polymers which are bonded together at their intersections. This bonding necessarily effects a rigidity and results in high cavity volume. As an improvement upon an earlier German utility patent which places the mat only at the bottom of a planting container, this version combines vertical and horizontal portions to line the interior bottom and sides of planting containers. The high cavity volume interstices of the vertical portion serve as pathways for evaporation of the excess water from the bottom of the container. Rather than being designed to cover a drain hole, this invention serves to compensate for the lack of one, none being shown in the patent drawings. Should this mat be applied over a drain hole, however, its rigidity and high cavity volume would allow direct fluid communication, resulting in soil erosion from the bottom of the container.
In contrast, U.S. Pat. No. 4,166,340 issued to Pluenneke on 4 Sep. 1979 employs a nonbiodegradable material and eliminates completely the rigidity and bonding of Schwartz and Herveling. Pluenneke employs the synthetic fiber fraction of discarded tires as an unbonded loose fill placed in the bottom of planting containers over the drain hole and beneath the soil. In his “Detailed Description of the Invention,” he offers that this material is retrievable directly from a large tire reclaiming facility, suggesting that this material might be an attractive option to large wholesale growers, but likely not the preferred choice of the average home gardener. But whether used by large wholesale growers or home gardeners, the loose fill nature of this fraction makes its retrieval, collection, and reuse difficult upon disassembling of filled container plantings. Therefore, an increasing quantity of this foreign nonbiodegradable substance might find its way into the larger environment.
The following three patents, while employing the preferred synthetic fiber and improving upon the uncontained loose fill of Pluenneke, nevertheless share the limiting factors of an abrupt change in particle size, non-universal application, and resulting cost and inconvenience to the consumer.
U.S. Pat. No. 5,181,951 issued to Cosse, Jr. on 26 Jan. 1993 employs nonwoven synthetic fabric, unspecified as to loft, to encase a packet of gravel and fertilizer for disposition in bottom of a planting container. Its side skirt extends vertically upward and communicates with the inner side wall and therefore must be produced—and purchased—in a plurality of sizes to correspond to different sizes of planting containers. Its complex construction will impact cost, as will its need to be replaced periodically as the fertilizer component is exhausted. Cost issue aside, the encased gravel layer effects an abrupt change in particle size from the soil mass, and will actually impede drainage, as described previously in this section.
The drain hole cover of U.S. Pat. No. 6,606,821 issued to Connelly on 19 Aug. 2003 is constructed as Cosse's, but includes no fertilizer. It specifies the encased layer to be a plurality of rocks, gravel, or nonabsorbent beads or pellets. With the exception of the exhaustibility of the fertilizer component, this device presents objections identical to those of Cosse's.
U.S. Pat. No. 7,877,930 B2 issued on 1 Feb. 2011 to Burge repeats the pouch construction and large-particle fill of Cosse and Connelly, improved by the possible addition of hydrophilic particles and a pot hole locator. Cosse, Connelly and Burge all compromise drainage by an abrupt change in particle size, and do not present a universal and inexpensive solution. They fail to address drain holes located partially or entirely in the container's vertical side walls, and must be purchased in a particular size relative to the planting container at hand.